Coating composition

ABSTRACT

A coating composition having (A) an alcohol dispersion which includes silica having the hydrophobic surface and dispersed in an alcohol dispersion medium, the content of silica in a solid substance being 80% by weight or more; (B) a solution including a silicone oligomer which is obtained by a reaction of an alkoxysilane with water and has an average structural unit represented by R 1   n SiO x/2 (OH) y  (OR 2)   z  (R 1  representing an alkyl group, phenyl group or vinyl group, R 2  representing an alkyl group and n, x, y and z representing numbers satisfying relations: 0.8≦n≦1.7, 2&lt;x&lt;3.2, y&gt;0, z&gt;0 and y+z=4−n−x); and (C) a curing agent. The coating composition exhibits excellent storage stability after the curing agent is added, suppresses aggregation of fine silica particles in spray coating and provides coating films having a high hardness and exhibiting excellent weatherability, water resistance, chemical resistance and adhesion.

TECHNICAL FIELD

The present invention relates to a coating composition and, moreparticularly, to a coating composition which can be prepared inaccordance with the sol-gel process and provides a coating film havingexcellent physical properties when the coating composition is applied tothe surface of metal, wood, paper, cloth, glass, ceramics, concrete or asynthetic resin by spray coating and cured at a low temperature in therange of the room temperature to about 200° C.

BACKGROUND ART

Heretofore, a coating material forming a coating layer having a highhardness and exhibiting excellent weatherability, water resistance,chemical resistance and adhesion at a low cost has been desired and manyproposals have been made. As an inorganic coating material, complexescomposed of sols of oxides and organosilanes which provideorgano-polysiloxanes by hydrolysis and polycondensation have mainly beenexamined.

For example, in Japanese Patent Application Laid-Open No. Showa57(1982)-165429, a coating process using an aqueous composition whichcontains a dispersion containing colloidal silica in a solution preparedby dissolving a partial condensate of a silanol into a mixture of analiphatic alcohol and water, a buffered latent catalyst for silanolcondensation and a β-hydroxyketone compound is proposed as a process forforming a coating layer which is cured in a short time and providesfastness and scratch resistance to the surface of plastic basematerials. In Japanese Patent Application Laid-Open No. Showa62(1987)-32157, a coating composition prepared by mixing anorganoalkoxysilane, an alcohol or a glycol, colloidal alumina, an acidand a filler insoluble in water is proposed as a coating composition forforming a coating layer exhibiting excellent heat resistance on thesurface of metal, cement and glass. In these coating compositions,alcohols are added in a great amount as hydrophilic organic solvents andwater is contained in a great amount as the dispersion medium of thesol. Therefore, these coating compositions have a drawback in that theconcentrations of solid substances is small and, moreover, the rates ofhydrolysis and polycondensation are very great and stability in storageis poor.

In Japanese Patent Application Laid-Open No. Showa 63(1988)-117074, acoating composition containing a condensate of an organoalkoxysilane,colloidal silica, water and a hydrophilic organic solvent is proposed asa coating composition which exhibits excellent storage stability andforms a coating layer having a high hardness and exhibiting excellentphysical properties on the surface of metal, ceramics and glass. Thiscoating composition has a drawback in that the composition tends tocause condensation of water on the surface due to a decrease in thetemperature by vaporization of the hydrophilic organic solvent duringspray coating. Aggregation of fine silica particles takes place due tothe condensation of water and it is difficult that a uniform coatinglayer is obtained. In Japanese Patent Application Laid-Open No. Heisei 4(1992)-175388, a coating composition containing, as the essentialcomponents, a solution of an oligomer of an organosilane in which silicais dispersed, a polyorganosiloxane having silanol group in the moleculeand a catalyst is proposed as a coating composition which is applied tothe surface of metal, concrete and plastic base materials, can be curedat a low temperature and can form a coating layer having a high hardnessand exhibiting excellent heat resistance and weatherability. Thiscoating composition has a drawback in that the pot life is short after acuring catalyst is added.

In Japanese Patent Application Laid-Open No. Heisei 3 (1991)-31380, acoating composition containing 30 to 90% by weight of a colloidal silicawhich has the surface modified with an alkoxysilane compound having 2 ormore alkoxyl groups and 70 to 10% by weight of a condensate of anorganotrialkoxysilane is proposed as a silicone coating compositionwhich forms a thick coating layer having a high hardness and exhibitingexcellent heat resistance, wear resistance, chemical resistance,weatherability and gloss on the surface of metal, ceramics, glass andcement and can be stored for a long time. This coating composition has adrawback in that, since water is added in combination with thealkoxysilane and/or condensates having low molecular weights thereofwhen the surface of the colloidal silica in this coating composition ismodified, hydrolysis and polycondensation of the alkoxysilane and/or thecondensates having low molecular weights thereof are promoted in thesolution and the efficiency of modification of the surface of thecolloidal silica decreases. Moreover, since this coating compositiondoes not contain curing catalysts, it takes a long time before theformed coating film is dried sufficiently so that the coating layer canbe touched by hands and, therefore, handling of the coated article isdifficult.

The present invention has an object of providing a coating compositionwhich exhibits excellent storage stability after addition of a curingagent, suppresses aggregation of fine silica particles during spraycoating and forms a coating layer having a high hardness and exhibitingexcellent weatherability, water resistance, chemical resistance andadhesion.

DISCLOSURE OF THE INVENTION

As the result of intensive studies by the present inventors to overcomethe above drawbacks, it was found that a coating composition comprisinga dispersion in an alcohol of fine silica particles which had thehydrophobic surface modified with a hydrocarbon group, a solutioncomprising a silicone oligomer which was obtained by the reaction of analkoxysilane with water and a curing agent had a long pot life afteraddition of the curing agent, suppressed aggregation of fine silicaparticles during spray coating and formed a coating layer exhibitingexcellent physical properties. The present invention has been completedbase on this knowledge.

The present invention provides:

(1) A coating composition which comprises:

(A) an alcohol dispersion which comprises silica having a hydrophobicsurface and dispersed in an alcohol dispersion medium and has a contentof silica in a solid substance of 80% by weight or more;

(B) a solution comprising a silicone oligomer which is obtained by areaction of an alkoxysilane with water and has an average structuralunit represented by:

R¹ _(n)SiO_(x/2)(OH)_(y)(OR²)z

wherein R¹ represents an alkyl group having 1 to 3 carbon atoms, phenylgroup or vinyl group, a plurality of R¹ may represent a same group ordifferent groups when the plurality of R¹ are present, R² represents analkyl group having 1 to 3 carbon atoms, a plurality of R² may representa same group or different groups when the plurality of R² are presentand n, x, y and z represent numbers satisfying relations of: 0.8≦n≦1.7,2<x<3.2, y>0, z>0 and y+z=4−n−x; and

(C) a curing agent;

(2) A coating composition described in (1), wherein a content ofcomponent (A) is 10 to 70% by weight as a solid substance and a contentof component (B) is 90 to 30% by weight as a solid substance each basedon a total amount of component (A) and component (B) as solid substancesand a content of component (C) is 1 to 40 parts by weight per 100 partsby weight of a total amount of component (A) and component (B) as solidsubstances;

(3) A coating composition described in (1), wherein the silica having ahydrophobic surface in component (A) is obtained by a reaction of finesilica particles with an organoalkoxysilane or an organohalosilane eachhaving a structure represented by:

R³ _(m)SiX_(4−m)

wherein R³ represents an alkyl group having 1 to 3 carbon atoms, phenylgroup or vinyl group, m represents 1, 2 or 3, a plurality of R³ mayrepresent a same group or different groups when m represents 2 or 3 andX represents Cl, OCH₃ or OC₂H₅;

(4) A coating composition described in (1), wherein the silica having ahydrophobic surface in component (A) is obtained by a reaction, in apresence of an amine-based silane coupling agent, of fine silicaparticles with an organoalkoxysilane having a structure represented by:

R³ _(m)SiX_(4−m)

wherein R³ represents an alkyl group having 1 to 3 carbon atoms, phenylgroup or vinyl group, m represents 1, 2 or 3, a plurality of R³ mayrepresent a same group or different groups when m represents 2 or 3 andX represents OCH₃ or OC₂H₅;

(5) A coating composition described in (1), wherein the siliconeoligomer in component (B) is prepared by using a metal chelate compoundas a catalyst;

(6) A coating composition described in (5), wherein a ligand of themetal chelate compound is at least one compound selected fromβ-diketones and cyclic polyethers having a large ring;

(7) A coating composition described in (1), wherein the siliconeoligomer in component (B) is prepared by using, as a self catalyst, asolution comprising a silicon compound which is soluble in a hydrophilicorganic solvent and has an average structural unit represented by:

R⁴ _(a)SiO_(b/2)(OH)_(C)(OR⁵⁾ _(d)

wherein R⁴ represents an alkyl group having 1 to 3 carbon atoms, phenylgroup or vinyl group, a plurality of R⁴ may represent a same group ordifferent groups when the plurality of R⁴ are present, R⁵ represents analkyl group having 1 to 3 carbon atoms, a plurality of R⁵ may representa same group or different groups when the plurality of R⁵ are presentand a, b, c and d represent numbers satisfying relations of: 0≦a<3,0<b<4, c>0, d≧0 and c+d=4−a−b;

(8) A coating composition described in (1), wherein component (C) is asolution comprising a complex having a structure represented by:

M(Che)_(p)(OR⁶)_(q)

wherein M represents a metal having a valence of 3 or greater, Cherepresents a chelating agent, R⁶ represents an alkyl group having 1 to 4carbon atoms, p represents a number of 1 or greater and q represents anumber of 2 or greater; or a polynuclear complex comprising said complexas a basic unit;

(9) A coating composition described in (8), wherein the chelating agentis a β-diketone; and

(10) A coating composition described in (1), wherein component (C)comprises a compound which is selected from carboxylic acids, alcoholshaving carbonyl group and alcohols having ether group and has a boilingpoint of 200° C. or lower.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

The coating composition of the present invention comprises (A) analcohol dispersion which comprises silica having the hydrophobic surfaceand dispersed in an alcohol dispersion medium and has a content ofsilica in the solid substance of 80% by weight or more, (B) a solutioncomprising a silicone oligomer which is obtained by the reaction of analkoxysilane with water and has an average structural unit representedby: R¹ _(n)SiO_(x/2)(OH)_(y)(OR²)_(z) and (C) a curing agent. In theabove structural formula, R¹ represents an alkyl group having 1 to 3carbon atoms, phenyl group or vinyl group, a plurality of R¹ mayrepresent the same group or different groups when the plurality of R¹are present, R² represents an alkyl group having 1 to 3 carbon atoms, aplurality of R² may represent the same group or different groups whenthe plurality of R² are present and n, x, y and z represent numberssatisfying relations of: 0.8≦n≦1.7, 2<x<3.2, y>0, z>0 and y+z=4−n−x. Theaverage structural unit means a structural unit of a silicone oligomeraveraged and expressed based on one Si atom.

In the present invention, the silica having the hydrophobic surface issilica in the form of fine particles which have the surface covered withan aliphatic, alicyclic or aromatic hydrocarbon group and exhibits adecreased affinity with water. In the composition of the presentinvention, the process for producing the alcohol dispersion whichcomprises silica having the hydrophobic surface and used as component(A) is not particularly limited. For example, the alcohol dispersionwhich comprises silica having the hydrophobic surface of the fine silicaparticles can be formed by adding an organoalkoxysilane or anorganohalosilane to an alcohol sol containing fine silica particlesdispersed in an alcohol dispersion medium, reacting theorganoalkoxysilane or the organohalosilane with water adsorbed on thefine silica particles and covering the surface of the fine silicaparticles with a hydrocarbon group to form the hydrophobic surface.Alternatively, the alcohol dispersion which comprises silica having thehydrophobic surface may be formed by covering the surface of the finesilica particles with a hydrocarbon group by reacting anorganoalkoxysilane or an organohalosilane with the fine silica particlesand, then, the obtained fine silica particles having the hydrophobicsurface may be dispersed in an alcohol dispersion medium. It ispreferable that the fine silica particles has diameters of 0.5 μm orsmaller. The alcohol used as the dispersion medium is not particularlylimited. Alcohols having a low boiling point such as methanol, ethanol,n-propanol and isopropanol are preferable since these alcohols vaporizeeasily during the coating operation.

Fine particles of other oxides such as alumina, titania and zirconia maybe used in place of fine particles of silica. Alcohol dispersionscontaining the fine particles of these oxides which have the hydrophobicsurface formed by the reaction with an organoalkoxysilane or anorganohalosilane may be used as component (A). From the standpoint oftransparency of the coating film, fine silica particles are preferableas the fine particles of oxides since the fine particles of silica havea refractive index closest to that of the organopolysiloxane which has alow refractive index.

As the alcohol sol in which fine silica particles are dispersed, acommercially available alcohol sol or a dispersion prepared bydispersing fine silica particles having diameters of 0.5 mm or smallerin an alcohol dispersion medium can be used. When an alcohol sol inwhich fine silica particles are dispersed is used, the surface of thefine silica particles can be made hydrophobic with a hydrocarbon groupby the reaction of an organoalkoxysilane or an organohalosilane withwater adsorbed on the surface. It is preferable that theorganoalkoxysilane or the organohalosilane used above is a compoundhaving a structure represented by R³ _(m)SiX_(4−m). In the formula, R³represents an alkyl group having 1 to 3 carbon atoms, phenyl group orvinyl group, m represents 1, 2 or 3, a plurality of R³ may represent thesame group or different groups when m represents 2 or 3 and X representsC1, OCH₃ or OC₂H₅. Examples of the organosilane include trialkoxysilanessuch as methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES),ethyltrimethoxysilane (ETMS), phenyltriethoxysilane (PhTES),vinyltriethoxysilane (VTES), n-propyl-trimethoxysilane (n-PrTMS) andisopropyltrimethoxysilane (iso-PrTMS); dialkoxysilanes such asdimethyldiethoxysilane (DMDE), diphenyldimethoxysilane (DPhDM) andmethylethyldimethoxysilane (MEDM); monoalkoxysilanes such astrimethylmethoxysilane (TMMS); and organochlorosilanes such asmethyltrichlorosilane, phenyltrichlorosilane, vinyltrichlorosilane,dimethyldichlorosilane, diphenyldichlorosilane andtrimethylchlorosilane. The organosilane can be used singly or incombination of two or more.

When the organoalkoxysilane or the organohalosilane is added to thealcohol sol in which fine silica particles are dispersed in an alcoholmedium, it is preferable that the organoalkoxysilane or theorganohalosilane is used in an amount which is the same as or more thanthe total amount of water adsorbed on the surface of the fine silicaparticles and water contained in the alcohol dispersion medium in asmall amount. When the reaction is conducted, it is preferable that careis taken as much as possible not to have water mixed into the dispersionmedium. When water is present in the dispersion medium in an excessamount, hydrolysis and polycondensation of the organoalkoxysilane or theorganohalosilane is promoted and the effect of forming the hydrophobicsurface on the fine silica particles is adversely affected. It ispreferable that an amine-based silane coupling agent is added tocomponent (A) in an amount of 0.1% by weight or less so that thereaction for forming the hydrophobic surface on the fine silicaparticles is promoted. The amine-based silane coupling agent used aboveis not particularly limited. Examples of the silane coupling agentinclude N-β-aminoethyl-γ-aminopropyltrimethoxysilane,N-β-aminoethyl-γ-aminopropylmethyl-dimethoxysilane andγ-aminopropyltriethoxysilane. When the amine-based silane coupling agentis added, it is preferable that an organoalkoxysilane is used as theagent for forming the hydrophobic surface on the fine silica particles.

In the composition of the present invention, the content of silica inthe solid substance is 80% by weight or more and preferably 85% or morein component (A). The silica in the solid substance means silicacontained in the alcohol sol before the organoalkoxysilane or theorganohalosilane is added. Silicon atoms bonded to the hydrocarbon groupwhich are derived from the organoalkoxysilane or the organohalosilaneare not include in the silica in the solid substance. When the amount ofsilica in the solid substance is less than 80% by weight, the relativeamount of the hydrophobic layer on the surface of the fine silicaparticles increases. As the result, unreacted alkoxyl groups andchlorine are left remaining in a great amount and there is thepossibility that the quality of the coating layer is adversely affected.

In the composition of the present invention, the fine silica particlescan be incorporated uniformly into the coating layer composed of anorganopolysiloxane due to the hydrophobic surface of the fine silicaparticles and a coating film having a high hardness and a greatmechanical strength and exhibiting excellent chemical durability can beobtained.

Component (B) used in the present invention is a solution comprising asilicone oligomer which is obtained by a reaction of an alkoxysilanewith water and has an average structural unit represented by R¹_(n)SiO_(x/2)(OH)_(y)(OR²)_(z). In the formula, R¹ represents an alkylgroup having 1 to 3 carbon atoms, phenyl group or vinyl group, aplurality of R¹ may represent the same group or different groups whenthe plurality of R¹ are present, R² represents an alkyl group having 1to 3 carbon atoms, a plurality of R² may represent the same group ordifferent groups when the plurality of R² are present and n, x, y and zrepresent numbers satisfying relations of: 0.8≦n≦1.7 and preferably1≦n≦1.3, 2<x<3.2 and preferably 2<x<3, y>0, z>0 and y+z=4−n−x. When thenumber represented by n is smaller than 0.8, it is difficult that stressis relaxed during drying the coating film and there is the possibilitythat cracks are formed in the coating film. When the number representedby n exceeds 1.7, the formation of a three-dimensional network structuretends to be difficult and there is the possibility that mechanicalproperties of the coating film deteriorates. When the number representedby x is smaller than 2, the formation of a linear polymer tends to bedifficult and there is the possibility that the amount of volatilecomponent increases. When the number represented by x exceeds 3.2, therelaxation of stress during drying the coating film tends to bedifficult and there is the possibility that cracks are formed in thecoating film. Since hydroxyl group in the silicone oligomer becomes thecrosslinking points in the crosslinking by the action of the curingagent, the presence of hydroxyl group is essential. The presence of thealkoxyl group represented by OR² is essential for maintaining thestorage stability of the solution before the addition of the curingagent.

The alkoxysilane used for the preparation of component (B) is notparticularly limited. Examples of the alkoxysilane includetetraalkoxysilanes such as tetramethoxysilane (TMOS) andtetraethoxy-silane (TEOS); trialkoxysilanes such asmethyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES),ethyltrimethoxysilane (ETMS), phenyltriethoxysilane (PhTES),vinyltriethoxysilane (VTES), n-propyl-trimethoxysilane (n-PrTMS) andisopropyltrimethoxysilane (iso-PrTMS); dialkoxysilanes such asdimethyldiethoxysilane (DMDE), diphenyldimethoxysilane (DPhDM) andmethylethyldimethoxysilane (MEDM); and monoalkoxysilanes such astrimethylmethoxysilane (TMMS).

In the preparation of component (B) used in the present invention, it ispreferable that water and the alkoxysilane are mixed in amounts suchthat the ratio of the amount by mole of H₂O to the amount by mole of Siis in the range of 1.4 to 4.0 and more preferably in the range of 1.4 to2.5 and the hydrolysis and the polycondensation are conducted. When theratio of the amount by mole of H₂O to the amount by mole of Si issmaller than 1.4, there is the possibility that the unreacted alkoxylgroup is left remaining in a great amount and the amount of the oligomerhaving high molecular weights decreases. Therefore, there is thepossibility that mechanical property of the coating film are adverselyaffected. When the ratio of the amount by mole of H₂O to the amount bymole of Si exceeds 4.0, water tends to be condensed on the surfaceduring the spray coating and there is the possibility that formation ofa uniform coating film becomes difficult during the film formation. Whenthe ratio of the amount by mole of H₂O to the amount by mole of Si isadjusted within the range of 1.4 to 4.0, a portion of the alkoxyl groupremains and the effect of improving the stability of the solutioncontaining the silicon oligomer of component (B) is exhibited.

In the preparation of component (B) of the composition of the presentinvention, it is preferable that an acid catalyst conventionally usedfor the sol-gel reaction is not used as the catalyst for the hydrolysisbut, instead, a metal chelate compound is used as the catalyst for thehydrolysis. When the acid catalyst is used, there is the possibilitythat gel tends to be formed. The metal chelate compound used as thecatalyst for the hydrolysis exhibits not only the catalytic effect onthe hydrolysis of alkoxide but also the effect of suppressingcrystallization when a methyltrialkoxysilane is used in a great amountas the raw material. Moreover, the metal chelate compound exhibits theeffect of promoting linear propagation of the polycondensation bydeprotonation of the silanol in addition to the catalytic effect on thehydrolysis. Therefore, the obtained liquid has excellent storagestability for a long time and the use of the metal chelate compound isadvantageous for the formation of a coating film. The metal chelatecompound is not particularly limited. Metal chelate compounds havingβ-diketones or cyclic polyethers having a large ring as the ligands canbe preferably used. The type of the metal ion is not particularlylimited. Metal ions having a great constant of complex formation withthe ligand are preferably used.

Examples of the metal chelate compound include metal chelate compoundsof β-diketones such as tris(acetylacetonato)aluminum(III), tris(ethylacetoacetato) aluminum(III), tris(diethyl malonato)aluminum(III)bis(acetylacetonato)copper(II), tetrakis(acetylacetonato)zirconium-(IV),tris(acetylacetonato)chromium(III), tris(acetylacetonato)cobalt(III) andtitanium(II) oxyacetylacetonate [(CH₃COCHCOCH₃)₂TiO]; metal chelatecompounds of β-diketones with rare earth metals; and metal chelatecompounds of cyclic polyethers having a large ring such as18-crown-6-potassium chelate compound salts, 12-crown-4-lithium chelatecompound salts and 15-crown-5-sodium chelate compound salts.

The amount of the metal chelate compound is not particularly limited andcan be suitably selected in accordance with the catalytic effect. Ingeneral, it is preferable that the amount is 0.001 to 5% by mole andmore preferably 0.005 to 1% by mole based on the amount of thealkoxysilane. When the amount of the metal chelate compound is less than0.001% by mole based on the amount of the alkoxysilane, there is thepossibility that the catalytic effect on the hydrolysis is not exhibitedsufficiently. When the amount of the metal chelate compound exceeds 5%by mole based on the amount of the alkoxysilane, there is thepossibility that the metal chelate compound is precipitated during theformation of a coating film and the properties of the coating film areadversely affected. When a self-catalyst is used, the amount of themetal chelate compound include the amount of the metal chelate compoundderived from the self-catalyst.

In the preparation of component (B) of the composition of the presentinvention, the alkoxysilane may be hydrolyzed and polycondensed by usinga solution comprising a silicon compound which has an average structuralunit represented by R⁴ _(a)SiO_(b/2)(OH)_(c)(OR⁵)_(d) and is soluble ina hydrophilic organic solvent as a self catalyst. In the formula, R⁴represents an alkyl group having 1 to 3 carbon atoms, phenyl group orvinyl group, a plurality of R⁴ may represent the same group or differentgroups when the plurality of R⁴ are present, R⁵ represents an alkylgroup having 1 to 3 carbon atoms, a plurality of R⁵ may represent thesame group or different groups when the plurality of R⁵ are present anda, b, c and d represent numbers satisfying relations of: 0≦a<3 andpreferably 0.8≦a<2, 0<b<4 and preferably 1<b<3, c>0, d<0 and c+d=4<a<b.The average structural unit means a structural unit of a siliconcompound averaged and expressed based on one Si atom. When the numberrepresented by a exceeds 3, the above silicon compound tend to bevaporized and there is the possibility that the silicon compound iscondensed and deactivated. When the number represented by c is greaterthan 0 and the silanol group is present, the hydrolysis of thealkoxysilane with water is promoted and polycondensation is alsopromoted due to protonation of the alkoxysilane with proton in thesilanol. The silicone oligomer itself in the solution of a siliconoligomer which is the product of the hydrolysis and the polycondensationof the alkoxysilane can be the above silicon compound having the aboveaverage structural unit represented by R⁴ _(a)SiO_(b/2)(OH)_(c)(OR⁵)_(d)which is used as the catalyst for the reaction. Therefore, this type ofthe catalyst is defines as a self-catalyst. It is preferable that theadded amount of the self-catalyst is in the range of 0.1 to 50% byweight and more preferably in the range of 1 to 40% by weight based onthe amount of the alkoxysilane. When the added amount of theself-catalyst is less than 0.1% by weight based on the amount of thealkoxysilane, the amount of transfer of proton is small and there is thepossibility that the efficiency of the hydrolysis decreases. When theadded amount of the self-catalyst exceeds 50% by weight based on theamount of the alkoxysilane, the amount of the silicone oligomer derivedfrom the catalyst increases in the solution of the silicone oligomerobtained by the reaction and there is the possibility that theefficiency of production of the silicone oligomer decreases. Moreover,there is the possibility that the quality of the obtained solution ofthe silicone oligomer becomes unstable.

When the solution of the self-catalyst is prepared from thealkoxysilane, it is preferable that at least one compound selected fromacids and metal chelate compounds is added as the catalyst. As the acid,an acid conventionally used in the sol-gel reaction, for example, an ainorganic acid such as nitric acid and hydrochloric acid and an organicacid such as acetic acid, can be used. When a coating film is formed onthe surface of a metal base material, it is preferable that a catalystof a metal chelate compound is used so that corrosion at the interfaceis suppressed. When a great amount of the self-catalyst is added in thepreparation of the solution of the silicone oligomer of the presentinvention, it is preferable that a catalyst of a metal chelate compoundis used since there is the possibility that the use of an acid catalystcauses deterioration in the storage stability.

A fresh solution of the self-catalyst can be prepared by hydrolysis andpolycondensation of an alkoxysilane using the solution of theself-catalyst thus obtained as the catalyst. In this case, it ispreferable that a catalyst of a metal chelate compound is used incombination.

The alkoxysilane used for the preparation of the solution of aself-catalyst is not particularly limited. Examples of the alkoxysilaneinclude tetraalkoxysilanes such as tetramethoxy-silane (TMOS) andtetraethoxysilane (TEOS); trialkoxysilanes such asmethyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES),ethyltrimethoxysilane (ETMS), phenyl-triethoxysilane (PhTES),vinyltriethoxysilane (VTES), n-propyl-trimethoxysilane (n-PrTMS) andisopropyltrimethoxysilane (iso-PrTMS); dialkoxysilanes such asdimethyldiethoxysilane (DMDE), diphenyl-dimethoxysilane (DPhDM) andmethylethyldimethoxysilane (MEDM); and monoalkoxysilanes such astrimethylmethoxysilane (TMMS).

The catalyst of a metal chelate compound used for preparation of thesolution of a self-catalyst is not particularly limited. Metal chelatecompounds having β-diketones and cyclic polyethers having a large ringcan be preferably used. The type of the metal ion is not particularlylimited. Metal ions having a great constant of complex formation withthe ligand can be preferably used. Examples of the metal chelatecompound include metal chelate compounds of β-diketones such astris(acetylacetonato)aluminum(III), tris(ethylacetoacetato)aluminum(III), tris(diethyl malonato)aluminum(III),bis(acetylacetonato)copper(II), tetrakis(acetylacetonato)zirconium(IV),tris(acetylacetonato)chromium(III), tris (acetylacetonato)cobalt(III)and titanium (II) oxyacetylacetonate [(CH₃COCHCOCH₃)₂TiO]; metal chelatecompounds of μ-diketones with rare earth metals; and metal chelatecompounds of cyclic polyethers having a large ring such as18-crown-6-potassium chelate compound salts, 12-crown-4-lithium chelatecompound salts and 15-crown-5-sodium chelate compound salts.

The amount of the catalyst of the metal chelate compound added in thepreparation of the solution of the self-catalyst is not particularlylimited and can be suitably selected in accordance with the catalyticeffect. In general, it is preferable that the amount is 0.001% by moleor more and more preferably 0.005% by mole or more based on the amountof the alkoxysilane. When the amount of the metal chelate compound isless than 0.001% by mole based on the amount of the alkoxysilane, thereis the possibility that the catalytic effect on the hydrolysis is notexhibited sufficiently. There is no upper limit in the amount of thecatalyst of the metal chelate compound based on the amount of thealkoxysilane as long as the metal chelate compound is homogeneouslydissolved.

In the composition of the present invention, a major portion of thesolvent of the solution comprising the silicone oligomer of component(B) is the alcohol formed by the hydrolysis of the alkoxysilane.Preparation of the solution of the silicone oligomer which is stable andhas a high concentration of solid substances is made possible byutilizing the alcohol formed by the hydrolysis without adding othersolvents. In the composition of the present invention, the molecularweight of the silicone oligomer is not particularly limited. A siliconeoligomer having a high molecular weight can be used as long as thesilicone oligomer formed by hydrolysis and polycondensation of thealkoxysilane is dissolved into the alcohol formed simultaneously and ahomogeneous solution is formed.

In the composition of the present invention, it is preferable that thecuring agent used as component (C) is a solution comprising a complexhaving the structure represented by M(Che)_(p)(OR⁶)_(q) or a polynuclearcomplex comprising the above complex as a basic unit. In the aboveformula, M represents a metal having a valence of 3 or greater, Cherepresents a chelating agent, R⁶ represents an alkyl group having 1 to 4carbon atoms, p represents a number of 1 or greater and q represents anumber of 2 or greater. In the composition of the present invention, thecuring agent of component (C) is added to a mixture of component (A) andcomponent (B) before the coating composition is used for the coating andexhibits the effect of promoting crosslinking in the process offormation of the coating film. The metal ion having a valence of 3 orgreater which is represented by M is not particularly limited. Examplesof the metal ion having a valence of 3 or greater include Al³⁺, Ti⁴⁺andZr⁴⁺. Examples of the reactive functional group represented by OR⁶include methoxyl group, ethoxyl group, n-propoxyl group, isopropoxylgroup, n-butoxyl group, secbutoxyl group and tert-butoxyl group. Whenthe number represented by q is 2 or greater, i.e., when the number ofthe reactive group represented by OR⁶ is 2 or greater, the curing agentexhibits the effect of promoting the crosslinking and a further effectof forming the crosslinking with the reactive group itself. Thechelating agent represented by Che is not particularly limited. Examplesof the chelating agent include acetylacetone, ethyl acetoacetate anddiethyl malonate.

In the composition of the present invention, it is preferable that thecuring agent of component (C) comprises a compound which is selectedfrom carboxylic acids, alcohols having carbonyl group and alcoholshaving ether group and has a boiling point of 200° C. or lower andpreferably 170° C. or lower. Examples of the above compound includecarboxylic acids such as formic acid, acetic acid, propionic acid,butyric acid, isobutyric acid, valeric acid, isovaleric acid, acrylicacid, isocrotonic acid and methacrylic acid; β-hydroxyketone compoundssuch as diacetone alcohol; alcohols having carbonyl group such asethylene glycol monoacetate; alcohols having ether group such asethylene glycol monomethyl ether, ethylene glycol monoethyl ether,2-(methoxymethoxy)ethanol, ethylene glycol monoisopropyl ether,propylene glycol monomethyl ether and propylene glycol monoethyl ether.The above compound can be used singly or in combination of two or more.

When the curing agent comprises a carboxylic acid, an alcohol havingcarbonyl group or an alcohol having ether group, this compound acts as astabilizer and the pot life of the coating composition comprisingcomponent (A), component (B) and component (C) increases to facilitatehandling. This compound exchanges the ligand with the group representedby OR⁶ in the compound represented by M(Che)_(p)(OR⁶)_(q) which is thecomponent of the curing agent. The stability of the curing agent isimproved by forming a partially chelated metal complex and, as theresult, the stability of the coating composition is improved. On theother hand, after the coating composition is applied and a coating filmis formed, the compound with which the ligand has been exchanged isremoved and the effect of promoting curing after the formation of thecoating film does not decrease. In this manner, a uniform coating filmhaving excellent mechanical properties can be obtained. It is preferablethat this compound is added in an amount of 0.5 moles or more per 1 moleof the metal represented by M. It is preferable that the curing isconducted at a temperature in the range of the room temperature to 200°C.

In the coating composition of the present invention, it is preferablethat the content of component (A) is 10 to 70% by weight as a solidsubstance and the content of component (B) is 90 to 30% by weight as asolid substance each based on the total amount of component (A) andcomponent (B) as solid substances. When the content of component (A) asa solid substance is smaller than 10% by weight or the content ofcomponent (B) as a solid substance exceeds 90% by weight based on thetotal amount of component (A) and component (B), there is thepossibility that hardness and mechanical strength of the coating filmdecrease. When the content of component (A) as a solid substance exceeds70% by weight or the content of component (B) as a solid substance issmaller than 30% by weight based on the total amount of component (A)and component (B), there is the possibility that the coating filmbecomes fragile due to the excessively small content of theorganopolysiloxane as the binder of the fine silica particles. It ismore preferable that the content of component (A) is 15 to 60% by weightas a solid substance and the content of component (B) is 85 to 40% byweight as a solid substance each based on the total amount of component(A) and component (B) as solid substances.

In the coating composition of the present invention, it is preferablethat the content of component (C) is 1 to 40 parts by weight per 100parts by weight of the total amount of component (A) and component (B)as solid substances. When the content of component (C) is smaller than 1part by weight per 100 parts by weight of the total amount of component(A) and component (B) as solid substances, there is the possibility thatcuring after the coating becomes insufficient. When the content ofcomponent (C) exceeds 40 part by weight per 100 parts by weight of thetotal amount of component (A) and component (B) as solid substances,there is the possibility that the pot life of the coating compositionobtained by mixing component (A), component (B) and component (C) isshort and there is the possibility that problems arise in the operation.It is more preferable that the content of component (C) is 2 to 25 partsby weight per 100 parts by weight of the total amount of component (A)and component (B) as solid substances.

The process for application of the coating composition of the presentinvention is not particularly limited and any conventional coatingprocess can be selected in accordance with the shape of the coatedarticle and the object of the coating. For example, any of the spraycoating process, the dipping coating process, the flow coating processand the roll coating process can be selected. The thickness of thecoating film can be selected in accordance with the object of coating.In general, it is preferable that the thickness is in the range of 1 to50 μm.

The coating composition of the present invention is applied to inorganicbase materials such as metal, glass, ceramics and concrete and organicbase materials such as acrylic resins, ABS resins, wood and paper toprotect the surface of the base materials and enhance the excellentappearance.

EXAMPLES

The present invention will be described more specifically with referenceto examples in the following. However, the present invention is notlimited to the examples.

In the examples, the evaluations of coating compositions and coatingfilms were conducted in accordance with the following methods. For theevaluation of a coating film, a coating film having a pencil scratchvalue of 3H or greater was used.

(1) Pencil Scratch Value

The pencil scratch value of a coating film formed on a steel plate wasevaluated in accordance with the method of Japanese Industrial StandardK5400 8.4.2.

(2) Water Permeability

The water permeability of a coating film formed on a cement board wasevaluated in accordance with the method of Japanese Industrial StandardK5400 8.16.

(3) Acid Resistance

The acid resistance of a coating film formed on a steel plate wasevaluated in accordance with the method of Japanese Industrial StandardK5400 8.22 by dipping into a 5% by weight/volume sulfuric acid kept at50° C. for 15 hours.

(4) Flexibility

The flexibility of a coating film formed on a steel plate was evaluatedin accordance with the method of Japanese Industrial Standard K5400 8.1using a stem having a diameter of 6 mm.

(5) Resistance to Repeated Cooling and Heating

The resistance to repeated cooling and heating of a coating film formedon a steel plate was evaluated in accordance with the method of JapaneseIndustrial Standard K5400 9.3 under repeated cooling and heating of 4cycles, each cycle being 120° C.×1 hour and −10° C.×1 hour.

(6) Water Resistance

The water resistance of a coating film formed on a glass plate wasevaluated in accordance with the method of Japanese Industrial StandardK5400 8.19 by dipping into deionized water kept at 60° C. for 7 days.

(7) Moisture Resistance

The moisture resistance of a coating film formed on a steel plate wasevaluated in accordance with the method of Japanese Industrial StandardK5400 9.2.1 for 7 days.

(8) Adhesion

The adhesion of a coating film formed on a steel plate was evaluated inaccordance with the method of Japanese Industrial Standard K5400 8.5.3.

(9) Weatherability Under an Accelerating Condition

The weatherability of a coating film formed on a steel plate under anaccelerating condition was evaluated in accordance with the method ofJapanese Industrial Standard K5400 9.8.1 for 500 hours.

(10) Storage Stability

A coating composition in an amount of 300 g prepared by mixingprescribed amounts of component (A), component (B) and component (C) wasplaced into a glass container of 500 ml. The glass container containingthe composition was sealed and placed into a chamber kept at 25° C. Thestorage stability was evaluated from the time by day during whichfluidity of the coating composition was maintained.

Preparation Example 1 Preparation of a Dispersion of Silica Having theHydrophobic Surface in an Alcohol)

To 100 parts by weight of silica sol containing isopropyl alcohol as thedispersion medium [manufactured by NISSAN CHEMICAL INDUSTRIES, Ltd.;IPA-ST; the solid content: 30% by weight], 10 parts by weight ofmethyltriethoxysilane [manufactured by SHIN-ETSU CHEMICAL Co., Ltd.;LS-1890] was mixed. The resultant mixture was left standing at 25° C.for 1 day and dispersion A-1 of silica having the hydrophobic surface inisopropyl alcohol was obtained. The surface of the fine powder of silicawas made hydrophobic with methyl group. The content of silica in thesolid substance of this dispersion was 89% by weight.

Preparation Example 2 Preparation of a Dispersion of Silica Having theHydrophobic Surface in an Alcohol

To 100 parts by weight of silica sol containing isopropyl alcohol as thedispersion medium [manufactured by NISSAN CHEMICAL INDUSTRIES, Ltd.;IPA-ST; the solid content: 30% by weight], 5 parts by weight ofmethyltriethoxysilane [manufactured by SHIN-ETSU CHEMICAL Co., Ltd.;LS-1890] was mixed. The resultant mixture was left standing at 25° C.for 1 day and dispersion A-2 of silica having the hydrophobic surface inisopropyl alcohol was obtained. The surface of the fine powder of silicawas made hydrophobic with methyl group. The content of silica in thesolid substance of this dispersion was 94% by weight.

Preparation Example 3 Preparation of a Dispersion of Silica Having theHydrophobic Surface in an Alcohol

Fine silica particles having an average diameter of 0.1 mm in an amountof 100 parts by weight was dispersed into 100 parts by weight of atoluene solution containing 10% by weight of methyltrichlorosilane[manufactured by SHIN-ETSU CHEMICAL Co., Ltd.; LS-40] and the formed gasof hydrochloric acid was neutralized with aqueous ammonia. Toluene wasremoved by distillation using an evaporator. After drying the residue,102 parts by weight of fine silica particles having the hydrophobicsurface was obtained. The obtained fine particles in an amount of 30parts by weight was dispersed in 70 parts by weight of isopropyl alcoholand dispersion A-3 of silica having the hydrophobic surface in isopropylalcohol was obtained. The surface of the fine powder of silica was madehydrophobic with methyl group. The content of silica in the solidsubstance of this dispersion was 98% by weight.

Preparation Example 4 Preparation of a Dispersion of Silica Having theHydrophobic Surface in an Alcohol

To 100 parts by weight of silica sol containing isopropyl alcohol as thedispersion medium [manufactured by NISSAN CHEMICAL INDUSTRIES, Ltd.;IPA-ST; the solid content: 30% by weight], 5 parts by weight ofmethyltriethoxysilane [manufactured by SHIN-ETSU CHEMICAL Co., Ltd.;LS-1890] and 0.05 parts by weight of y-aminopropyltriethoxysilane[manufactured by SHIN-ETSU CHEMICAL Co., Ltd.; KBE903] were mixed. Theresultant mixture was left standing at 25° C. for 1 day and dispersionA-4 of silica having the hydrophobic surface in isopropyl alcohol wasobtained. The surface of the fine powder of silica was made hydrophobicwith methyl group. The content of silica in the solid substance of thisdispersion was 94% by weight.

Preparation Example 5 Preparation of a Solution of a Silicone Oligomer

To 100 parts by weight of methyltriethoxysilane [manufactured bySHIN-ETSU CHEMICAL Co., Ltd.; LS-1890], 0.02 parts by weight oftris(acetylacetonato)aluminum(III) [manufactured by DOJIN KAGAKUKENKYUSHO Co., Ltd.] was added. The reaction was allowed to proceed inthe resultant solution at 50° C. for 1 day while 18 parts by weight ofdistilled water was added to the solution and transparent solution B-1of a silicone oligomer was obtained. The solid content of this solutionof the silicone oligomer was 32% by weight.

Preparation Example 6 Preparation of a Solution of a Silicone Oligomer

To a mixture of 100 parts by weight of methyltriethoxysilane[manufactured by SHIN-ETSU CHEMICAL Co., Ltd.; LS-1890] and 83 parts byweight of dimethyldiethoxysilane [manufactured by SHIN-ETSU CHEMICALCo., Ltd.; LS-1370], 0.04 parts by weight oftris-(acetylacetonato)aluminum(III) [manufactured by DOJIN KAGAKUKENKYUSHO Co., Ltd.] was added. The reaction was allowed to proceed inthe resultant solution at 50° C. for 1 day while 30 parts by weight ofdistilled water was added to the solution and transparent solution B-2of a silicone oligomer was obtained. The solid content of this solutionof the silicone oligomer was 37% by weight.

Preparation Example 7 Preparation of a Solution of a Silicone Oligomer

To a mixed solution of 100 parts by weight of methyltriethoxysilane[manufactured by SHIN-ETSU CHEMICAL Co., Ltd.; LS-1890] and 25 parts byweight of ethanol, 0.06 parts by weight oftris(acetylacetonato)-aluminum(III) [manufactured by DOJIN KAGAKUKENKYUSHO Co., Ltd.] was added. The resultant mixture was stirred at theroom temperature for 30 minutes and tris(acetylacetonato)aluminum(III)was dissolved. Then, 18 parts by weight of distilled water was added tothe resultant solution over 1 hour while the solution was stirred. Theresultant solution was then left standing at the room temperature for 1day and the obtained solution was used as self-catalyst A.

To 100 parts by weight of methyltriethoxysilane [manufactured bySHIN-ETSU CHEMICAL Co., Ltd.; LS-1890], 28 parts by weight ofself-catalyst A prepared above was added and then 0.02 parts by weightof tris(acetylacetonato)aluminum(III) [manufactured by DOJIN KAGAKUKENKYUSHO Co., Ltd.] was added. The resultant mixture was stirred at theroom temperature for 30 minutes and tris(acetylacetonato)-aluminum(III)was dissolved. Then, 18 parts by weight of distilled water was added tothe resultant solution over 1 hour while the solution was stirred. Theresultant solution was left standing at the room temperature for 1 dayand homogeneous solution B-3 of a silicone oligomer was obtained. Thesolid content of this solution of the silicone oligomer was 31% byweight.

Preparation Example 8 Preparation of a Curing Agent

With 100 parts by weight of aluminum tri-sec-butoxide [manufactured byKANTO KAGAKU Co., Ltd.], 40.5 parts by weight of acetylacetone, 50 partsby weight of acetic acid and 200 parts by weight of ethanol were mixedand curing agent C-1 was obtained.

Preparation Example 9 Preparation of a Curing Agent

With 100 parts by weight of aluminum tri-sec-butoxide [manufactured byKANTO KAGAKU Co., Ltd.], 40.5 parts by weight of acetylacetone and 240parts by weight of diacetone alcohol were mixed and curing agent C-2 wasobtained.

Preparation Example 10 Preparation of a Curing Agent

With 100 parts by weight of titanium tetra-n-butoxide [manufactured byKANTO KAGAKU Co., Ltd.], 29.4 parts by weight of acetylacetone, 9 partsby weight of acetic acid and 170 parts by weight of ethylene glycolmonomethyl ether were mixed and curing agent C-3 was obtained.

Example 1

Dispersion A-1 of silica having the hydrophobic surface in isopropylalcohol in an amount of 20 parts by weight, 80 parts by weight ofsolution B-1 of a silicone oligomer and 4 parts by weight of curingagent C-1 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 8 μm were formed. A transparent coatingfilm having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be H and, after the coatingfilm was further heated at 80° C. for 1 hour, the pencil scratch valuewas found to be 5H. The water permeability was 10 ml/m².day or smaller.In the test of the acid resistance, no crack, cleavage, hole, softeningor rust was observed. The dipping solution showed no coloring orturbidity and the coating film exhibited no change in the gloss afterthe test. In the test of the flexibility, no crack or cleavage wasobserved. In the test of the repeated cooling and heating, no crack,cleavage, swelling or whitening was observed. In the test of the waterresistance, no wrinkle, swelling, crack, cleavage, change in gloss,clouding, whitening or discoloration was observed. In the test of themoisture resistance, no wrinkle, swelling, crack, rust, cleavage,clouding or whitening was observed. In the test of the adhesion, nocleavage was observed at all. In the accelerated test of theweatherability, no discoloration or formation of cracks was observed. Inthe test of the storage stability, no change in the fluidity wasobserved for 7 days. On the eighth day, gel was formed and the fluiditywas lost.

Example 2

Dispersion A-1 of silica having the hydrophobic surface in isopropylalcohol in an amount of 50 parts by weight, 50 parts by weight ofsolution B-1 of a silicone oligomer and 3 parts by weight of curingagent C-1 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 8 μm were formed. A transparent coatingfilm having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be 2H and, after the coatingfilm was further cured at the room temperature for 1 month, the pencilscratch value was found to be 6H. The water permeability was 10ml/m².day or smaller. In the test of the acid resistance, no crack,cleavage, hole, softening or rust was observed. The dipping solutionshowed no coloring or turbidity and the coating film exhibited no changein the gloss after the test. In the test of the flexibility, no crack orcleavage was observed. In the test of the repeated cooling and heating,no crack, cleavage, swelling or whitening was observed. In the test ofthe water resistance, no wrinkle, swelling, crack, cleavage, change ingloss, clouding, whitening or discoloration was observed. In the test ofthe moisture resistance, no wrinkle, swelling, crack, rust, cleavage,clouding or whitening was observed. In the test of the adhesion, nocleavage was observed at all. In the accelerated test of theweatherability, no discoloration or formation of cracks was observed. Inthe test of the storage stability, no change in the fluidity wasobserved for 10 days. On the eleventh day, gel was formed and thefluidity was lost.

Example 3

Dispersion A-1 of silica having the hydrophobic surface in isopropylalcohol in an amount of 20 parts by weight, 80 parts by weight ofsolution B-1 of a silicone oligomer and 4 parts by weight of curingagent C-2 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 5 μm were formed. A transparent coatingfilm having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be 4H. The waterpermeability was 10 ml/m².day or smaller. In the test of the acidresistance, no crack, cleavage, hole, softening or rust was observed.The dipping solution showed no coloring or turbidity and the coatingfilm exhibited no change in the gloss after the test. In the test of theflexibility, no crack or cleavage was observed. In the test of therepeated cooling and heating, no crack, cleavage, swelling or whiteningwas observed. In the test of the water resistance, no wrinkle, swelling,crack, cleavage, change in gloss, clouding, whitening or discolorationwas observed. In the test of the moisture resistance, no wrinkle,swelling, crack, rust, cleavage, clouding or whitening was observed. Inthe test of the adhesion, no cleavage was observed at all. In theaccelerated test of the weatherability, no discoloration or formation ofcracks was observed. In the test of the storage stability, no change inthe fluidity was observed for 5 days. On the sixth day, gel was formedand the fluidity was lost.

Example 4

Dispersion A-2 of silica having the hydrophobic surface in isopropylalcohol in an amount of 20 parts by weight, 80 parts by weight ofsolution B-1 of a silicone oligomer and 4 parts by weight of curingagent C-2 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 6 μm were formed. A transparent coatingfilm having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be 4H. The waterpermeability was 10 ml/m².day or smaller. In the test of the acidresistance, no crack, cleavage, hole, softening or rust was observed.The dipping solution showed no coloring or turbidity and the coatingfilm exhibited no change in the gloss after the test. In the test of theflexibility, no crack or cleavage was observed. In the test of therepeated cooling and heating, no crack, cleavage, swelling or whiteningwas observed. In the test of the water resistance, no wrinkle, swelling,crack, cleavage, change in gloss, clouding, whitening or discolorationwas observed. In the test of the moisture resistance, no wrinkle,swelling, crack, rust, cleavage, clouding or whitening was observed. Inthe test of the adhesion, no cleavage was observed at all. In theaccelerated test of the weatherability, no discoloration or formation ofcracks was observed. In the test of the storage stability, no change inthe fluidity was observed for 5 days. On the sixth day, gel was formedand the fluidity was lost.

Example 5

Dispersion A-1 of silica having the hydrophobic surface in isopropylalcohol in an amount of 50 parts by weight, 50 parts by weight ofsolution B-2 of a silicone oligomer and 5 parts by weight of curingagent C-2 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 20 μm were formed. A transparentcoating film having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be H and, after the coatingfilm was further heated at 80° C. for 1 hour, the pencil scratch valuewas found to be 3H. The water permeability was 10 ml/m².day or smaller.In the test of the acid resistance, no crack, cleavage, hole, softeningor rust was observed. The dipping solution showed no coloring orturbidity and the coating film exhibited no change in the gloss afterthe test. In the test of the flexibility, no crack or cleavage wasobserved. In the test of the repeated cooling and heating, no crack,cleavage, swelling or whitening was observed. In the test of the waterresistance, no wrinkle, swelling, crack, cleavage, change in gloss,clouding, whitening or discoloration was observed. In the test of themoisture resistance, no wrinkle, swelling, crack, rust, cleavage,clouding or whitening was observed. In the test of the adhesion, nocleavage was observed at all. In the accelerated test of theweatherability, no discoloration or formation of cracks was observed. Inthe test of the storage stability, no change in the fluidity wasobserved for 10 days. On the eleventh day, gel was formed and thefluidity was lost.

Example 6

Dispersion A-2 of silica having the hydrophobic surface in isopropylalcohol in an amount of 50 parts by weight, 50 parts by weight ofsolution B-1 of a silicone oligomer and 5 parts by weight of curingagent C-3 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 15 μm were formed. A transparentcoating film having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be 2H and, after the coatingfilm was further heated at 80° C. for 1 hour, the pencil scratch valuewas found to be 7H. The water permeability was 10 ml/m².day or smaller.In the test of the acid resistance, no crack, cleavage, hole, softeningor rust was observed. The dipping solution showed no coloring orturbidity and the coating film exhibited no change in the gloss afterthe test. In the test of the flexibility, no crack or cleavage wasobserved. In the test of the repeated cooling and heating, no crack,cleavage, swelling or whitening was observed. In the test of the waterresistance, no wrinkle, swelling, crack, cleavage, change in gloss,clouding, whitening or discoloration was observed. In the test of themoisture resistance, no wrinkle, swelling, crack, rust, cleavage,clouding or whitening was observed. In the test of the adhesion, nocleavage was observed at all. In the accelerated test of theweatherability, no discoloration or formation of cracks was observed. Inthe test of the storage stability, no change in the fluidity wasobserved for 10 days. On the eleventh day, gel was formed and thefluidity was lost.

Example 7

Dispersion A-3 of silica having the hydrophobic surface in isopropylalcohol in an amount of 50 parts by weight, 50 parts by weight ofsolution B-1 of a silicone oligomer and 5 parts by weight of curingagent C-3 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 15 μm were formed. A translucentcoating film having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be 2H and, after the coatingfilm was further heated at 80° C. for 1 hour, the pencil scratch valuewas found to be 7H. The water permeability was 10 ml/m².day or smaller.In the test of the acid resistance, no crack, cleavage, hole, softeningor rust was observed. The dipping solution showed no coloring orturbidity and the coating film exhibited no change in the gloss afterthe test. In the test of the flexibility, no crack or cleavage wasobserved. In the test of the repeated cooling and heating, no crack,cleavage, swelling or whitening was observed. In the test of the waterresistance, no wrinkle, swelling, crack, cleavage, change in gloss,clouding, whitening or discoloration was observed. In the test of themoisture resistance, no wrinkle, swelling, crack, rust, cleavage,clouding or whitening was observed. In the test of the adhesion, nocleavage was observed at all. In the accelerated test of theweatherability, no discoloration or formation of cracks was observed. Inthe test of the storage stability, no change in the fluidity wasobserved for 10 days. On the eleventh day, gel was formed and thefluidity was lost.

Example 8

Dispersion A-1 of silica having the hydrophobic surface in isopropylalcohol in an amount of 20 parts by weight, 80 parts by weight ofsolution B-3 of a silicone oligomer and 4 parts by weight of curingagent C-3 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 12 μm were formed. A transparentcoating film having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be H and, after the coatingfilm was further heated at 80° C. for 1 hour, the pencil scratch valuewas found to be 5H. The water permeability was 10 ml/m².day or smaller.In the test of the acid resistance, no crack, cleavage, hole, softeningor rust was observed. The dipping solution showed no coloring orturbidity and the coating film exhibited no change in the gloss afterthe test. In the test of the flexibility, no crack or cleavage wasobserved. In the test of the repeated cooling and heating, no crack,cleavage, swelling or whitening was observed. In the test of the waterresistance, no wrinkle, swelling, crack, cleavage, change in gloss,clouding, whitening or discoloration was observed. In the test of themoisture resistance, no wrinkle, swelling, crack, rust, cleavage,clouding or whitening was observed. In the test of the adhesion, nocleavage was observed at all. In the accelerated test of theweatherability, no discoloration or formation of cracks was observed. Inthe test of the storage stability, no change in the fluidity wasobserved for 8 days. On the ninth day, gel was formed and the fluiditywas lost.

Example 9

Dispersion A-4 of silica having the hydrophobic surface in isopropylalcohol in an amount of 50 parts by weight, 50 parts by weight ofsolution B-1 of a silicone oligomer and 5 parts by weight of curingagent C-3 were mixed together and a coating composition was obtained.The obtained coating composition was applied to steel plates (thethickness: 0.3 mm and 0.8 mm), an aluminum plate, a glass plate (thethickness: 2 mm), a cement board (the thickness: 8 mm) and a methacrylicresin plate in accordance with the spray coating process and coatingfilms each having a thickness of 12 μm were formed. A transparentcoating film having gloss was obtained on each plate.

After the coating film was left standing at the room temperature for 2days, the pencil scratch value was found to be 2H and, after the coatingfilm was further heated at 80° C. for 1 hour, the pencil scratch valuewas found to be 7H. The water permeability was 10 ml/m².day or smaller.In the test of the acid resistance, no crack, cleavage, hole, softeningor rust was observed. The dipping solution showed no coloring orturbidity and the coating film exhibited no change in the gloss afterthe test. In the test of the flexibility, no crack or cleavage wasobserved. In the test of the repeated cooling and heating, no crack,cleavage, swelling or whitening was observed. In the test of the waterresistance, no wrinkle, swelling, crack, cleavage, change in gloss,clouding, whitening or discoloration was observed. In the test of themoisture resistance, no wrinkle, swelling, crack, rust, cleavage,clouding or whitening was observed. In the test of the adhesion, nocleavage was observed at all. In the accelerated test of theweatherability, no discoloration or formation of cracks was observed. Inthe test of the storage stability, no change in the fluidity wasobserved for 9 days. On the tenth day, gel was formed and the fluiditywas lost.

Comparative Example 1

A silica sol in isopropyl alcohol as the dispersion medium [manufacturedby NISSAN CHEMICAL INDUSTRIES, Ltd.; IPA-ST; solid content: 30% byweight] in an amount of 40 parts by weight, 60 parts by weight ofsolution B-1 of a silicone oligomer and 3 parts by weight of curingagent C-1 were mixed together and a coating composition was obtained.The obtained coating composition was applied to a steel plate (thethickness: 0.8 mm) in accordance with the spray coating process.Numerous grains were observed on the surface and no uniform coating filmwas obtained. Therefore, evaluations of the coating film was notconducted.

The results of Examples 1 to 9 and Comparative Example 1 are shown inTable 1.

TABLE 1-1 Water Pencil permea- scratch bility Acid Curing conditionvalue (ml/m²·day) resistance Flexibility Example 1 room temp. × 2 days H<10 good good 80° C. × 1 hour 5 H Example 2 room temp. × 2 days 2 H <10good good room temp. × 1 month 6 H Example 3 room temp. × 2 days 4 H <10good good Example 4 room temp. × 2 days 4 H <10 good good Example 5 roomtemp. × 2 days H <10 good good 80° C. × 1 hour 3 H Example 6 room temp.× 2 days 2 H <10 good good 80° C. × 1 hour 7 H Example 7 room temp. × 2days 2 H <10 good good 80° C. × 1 hour 7 H Example 8 room temp. × 2 daysH <10 good good 80° C. × 1 hour 5 H Example 9 room temp. × 2 days 2 H<10 good good 80° C. × 1 hour 7 H Comparative No uniform coating filmformed Example 1

TABLE 1-2 Resistance Weather- to repeated ability in Storage cooling andWater Moisture Adhesion accelerated stability heating resistanceresistance (point) test (day) Example 1 good good good 10 good 7 Example2 good good good 10 good 10 Example 3 good good good 10 good 5 Example 4good good good 10 good 5 Example 5 good good good 10 good 10 Example 6good good good 10 good 10 Example 7 good good good 10 good 10 Example 8good good good 10 good 8 Example 9 good good good 10 good 9 ComparativeNo uniform coating film formed Example 1

As shown in Table 1, the coating compositions of the present inventionwere kept fluid for 5 to 10 days after the curing agent was mixed andcould be used for coating. Therefore, the coating compositions exhibitedexcellent workability and could be handled easily. Since the obtainedcoating films all exhibited excellent gloss and were transparent ortranslucent, the coating compositions could keep the excellentappearance when the compositions were applied to steel plates, analuminum plate, a cement board, a glass plate and a methacrylic resinplate. The coating films exhibited excellent physical properties such asa high hardnesses, small water permeability and excellent acidresistance, flexibility, resistance to repeated cooling and heating,water resistance, moisture resistance, adhesion and weatherability andcould protect the base material of the coating for a long time.

INDUSTRIAL APPLICABILITY

The coating composition of the present invention exhibits excellentstorage stability after the addition of the curing agent, suppressesaggregation of fine silica particles during spray coating and can form acoating film having a high hardness and exhibiting excellentweatherability, water resistance, chemical resistance and adhesion whenthe coating composition is applied to the surface of base materials suchas metal, wood, paper, cloth, glass, ceramics, concrete and syntheticresins.

What is claimed is:
 1. A coating composition which comprises: (A) analcohol dispersion which comprises silica having a hydrophobic surfaceand dispersed in an alcohol dispersion medium and has a content ofsilica in a solid substance of 80% by weight or more; (B) a solutioncomprising a silicone oligomer which is obtained by a reaction of analkoxysilane with water and has an average structural unit representedby: R¹ _(n)SiO_(x/2)(OH)_(y)(OR²)_(z) wherein R¹ represents an alkylgroup having 1 to 3 carbon atoms, phenyl group or vinyl group, aplurality of R¹ may represent a same group or different groups when theplurality of R¹ are present, R² represents an alkyl group having 1 to 3carbon atoms, a plurality of R² may represent a same group or differentgroups when the plurality of R² are present and n, x, y and z representnumbers satisfying relations of: 0.8≦n≦1.7, 2<x<3.2, y>0, z>0 andy+z=4−n−x; and (C) a curing agent.
 2. A coating composition according toclaim 1, wherein a content of component (A) is 10 to 70% by weight as asolid substance and a content of component (B) is 90 to 30% by weight asa solid substance each based on a total amount of component (A) andcomponent (B) as solid substances and a content of component (C) is 1 to40 parts by weight per 100 parts by weight of a total amount ofcomponent (A) and component (B) as solid substances.
 3. A coatingcomposition according to claim 1, wherein the silica having ahydrophobic surface in component (A) is obtained by a reaction of finesilica particles with an organoalkoxysilane or an organohalosilane eachhaving a structure represented by: R³ _(m)SiX_(4−m) wherein R³represents an alkyl group having 1 to 3 carbon atoms, phenyl group orvinyl group, m represents 1, 2 or 3, a plurality of R³ may represent asame group or different groups when m represents 2 or 3 and X representsCl, OCH₃ or OC₂H₅.
 4. A coating composition according to claim 1,wherein the silica having a hydrophobic surface in component (A) isobtained by a reaction, in a presence of an amine-based silane couplingagent, of fine silica particles with an organoalkoxysilane having astructure represented by: R³ _(m)SiX_(4−m) wherein R³ represents analkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, mrepresents 1, 2 or 3, a plurality of R³ may represent a same group ordifferent groups when m represents 2 or 3 and X represents OCH₃ orOC₂H₅.
 5. A coating composition according to claim 1, wherein thesilicone oligomer in component (B) is prepared by using a metal chelatecompound as a catalyst.
 6. A coating composition according to claim 5,wherein a ligand of the metal chelate compound is at least one compoundselected from β-diketones and cyclic polyethers having a large ring,wherein said cyclic polyethers are selected from the group consisting of18-crown-6-potassium chelate compound salts, 12-crown-4-lithium chelatecompound salts and 15-crown-5-sodium chelate compound salts.
 7. Acoating composition according to claim 1, wherein the silicone oligomerin component (B) is prepared by using, as a self catalyst, a solutioncomprising a silicon compound which is soluble in a hydrophilic organicsolvent and has an average structural unit represented by: R⁴_(a)SiO_(b/2)(OH)_(c)(OR⁵)_(d) wherein R⁴ represents an alkyl grouphaving 1 to 3 carbon atoms, phenyl group or vinyl group, a plurality ofR⁴ may represent a same group or different groups when the plurality ofR⁴ are present, R⁵ represents an ialkyl group having 1 to 3 carbonatoms, a plurality of R⁵ may represent a same group or different groupswhen the plurality of R⁵ are present and a, b, c and d represent numberssatisfying relations of: 0≦a<3, 0<b<4, c>0, d≧0 and c+d=4−a−b.
 8. Acoating composition according to claim 1, wherein component (C) is asolution comprising a complex having a structure represented by:M(Che)_(p)(OR⁶)_(q) wherein M represents a metal having a valence of 3or greater, Che represents a chelating agent, R⁶ represents an alkylgroup having 1 to 4 carbon atoms, p represents a number of 1 or greaterand q represents a number of 2 or greater; or a polynuclear complexcomprising said complex as a basic unit.
 9. A coating compositionaccording to claim 8, wherein the chelating agent is a β-diketone.
 10. Acoating composition according to claim 1, wherein component (C)comprises a compound which is selected from carboxylic acids, alcoholshaving carbonyl group and alcohols having ether group and has a boilingpoint of 200° C. or lower.